Law
The Principle of Proportionality in Self-Defense under International Law
Quick fact
Under international law, self-defense must be proportionate to the armed attack, meaning a response cannot exceed what is needed to repel the attack. This was confirmed in the ICJ's Nicaragua and Oil Platforms cases, which found that even a significant attack may not justify a massive retaliation.
Why this is interesting
When a nation is attacked, it may fight back—but how much force is too much? The principle of proportionality draws a line that separates lawful defense from unlawful aggression.